Ideal Multimeters

Basic measurements:

Before looking at other features make sure the meter covers the ranges you need from min to max.

Safety, Safety, Safety!

When choosing a multimeter, first determine CAT levels you will be operating. Then choose a meter with a voltage rating higher than the maximum voltage you will be testing at each CAT level. For example, an electrician working in CAT III and CAT IV areas can choose a meter rated CAT III 1000 V / CAT IV 600 V. Within a category, a higher voltage rating denotes a higher transient withstand rating, e.g., a CAT III-1000 V meter has superior protection compared to a CAT III-600 V rated meter. The real misunderstanding occurs if someone selects a CAT II-1000 V rated meter thinking that it is superior to a CAT III-600 V meter. Select a meter with the voltage rating suitable for the location (i.e. CAT I, II, III, IV) where you will be operating.
 

Photo from Fluke's "ABCs of Multimeter Safety" showing locations where CAT ratings I - IV apply Click photo to download the Application Note

Here are useful articles from FLUKE on TRMS and the errors of not having a True RMS meter:
Facts About True RMS Measurement          Why True RMS?

 

Consider the extras...

Clear big digits and backlight for visibility. You will appreciate it next time you are in low-visibility conditions. Ideal meters incorporate these features.

Min/Max/Peak Hold. Free you hands and eliminate the need to watch the display closely by capturing min/max/hold at the touch of a button. Ideal meters have this feature as well as an "Auto Hold" function.

Relative Mode/Measurement feature permits making measurements relative to a stored reference value. The displayed value is the difference between the reference value and measured value. It can be particularly useful when measuring voltage or resistance. A press of the relative button can zero out the resistance of voltage probes. Look for this feature on most Ideal DMMs.

Temperature Measurement. This can be a very convenient feature to have and is a must-have for HVAC technicians. Most Ideal DMMs incorporate this feature.

Low Input Impedance (LoZ). Certain Ideal DMM's will have a rotary switch position labeled Auto - VLoZ which will have a low input impedance for AC voltage measurements with automatic voltage detection.

Non-Contact Voltage Detector. These are typically purchased separately as inexpensive test pens but some multimeters from Ideal have this as a built-in function. Essentially this allows the DMM to sense the electric field around energized AC circuits which is useful troubleshooting. A visible light and audible beep would typically indicate an energized circuit.

Datalogging and PC connectivity. Troubleshoot intermittent problems and datalog high energy circuits from a safe distance. Most Ideal digital multimeters feature datalogging functions up to a maximum of 20,000 records. Data can then be transfered to PC via the included USB cable.

Build Quality. Meters above $100-200 will have better durability, fit and finish. The rotary dial will feel better and not permit landing in between settings. Probes will be insulated with silicone instead of PVC, some have CAT ratings printed right on the leads. Probe handles are bigger and tips sharper. Watch the comparison videos below to get a better idea of how important this is.

What are Digits on a multimeter?

Digits refers to the resolution of the DMM, not the accuracy. It is common to see meter specifications with 3-½, 3-¾, 4-½, etc. digit display. The half means the most significant digit can go up to 1. It originated because of  7-segment LCD/LED  displays. All 7 segments are needed to display every digit. When for the most significant digit on the far left only 1 is to be displayed, only the two rightmost segments of the 7 are needed, hence the term ½ digit originated (i.e. a fraction of the 7 segments are used, very loosely approximated as a half). That was when most DMMs had a maximum reading of 1999. Recently more accurate DMMs became available, having readings up to 2999, or 3999, even 4999, so it became more complicated. Manufacturers started using the ¾ approximation. But still not very clear as you can see here

Use of Counts eliminates the fractional confusion of the Digits terminology
 

So what happens as the measurement goes up in value?
For example, a 3-½  digit, 2000 count meter is measuring 1.999 volts. Increasing the voltage to 2.532 volts results in a loss of the least significant digit. The display will read 2.53 Volts. One digit of resolution is lost.

What about Multimeter Accuracy?
Accuracy is not the same as resolution. Resolution as explained above has to do with the number of visible digits (i.e. to the right of the decimal). Accuracy has to do with how correct or true the value is compared to a standard value from NIST or other international body. Look back at the snapshot from the video blog of David Jones above. He gives a simple formula using counts to give a rough minimum accuracy. David warns against meters that have a published accuracy higher than the minimums on his chart for the count level. See the video in full below.

Quick Question: I often see an accuracy specification like this 1% of reading + 3 counts (or digits). How can I tell what my margin of error would be?

A: It refers to the least significant digit on the meter on that range. As an example, lets work the math for measuring 120 volts ac on a 6000 count meter (remember, it therefore goes from 0 to 5999). To measure 120 volts ac, the meter will have to be on the 600.0 ac voltage range. The resolution (least significant digit) then is 0.1 volt. (120 V X 1% = 1.2 V + 3 digits) = (1.2 V + 0.3 v). Therefore the margin of error would be +/- 1.5 V.

Video blogger David Jones (EEVBlog.com ) “Digital Multimeter Buying Guide for Beginners” has 100,000+ views. He covers safety, accuracy, ruggedness, important to obscure features, takes apart popular models, and more in his colorful and funny style.

This 30 min Fluke Electrical Measurement Safety video gives life saving  advice when using meters. In the Meter testing tab, poorly designed meters are tested and shown sparking even catching fire compared to properly designed and fused meters .  It really illustrates the importance of not only having the proper CAT rating, but checking that the meter has independent safety approvals such as UL. If you do not see the approval in the data sheet, check the instruction manual, or ask our sales team.

Click here to see the video